In the industrial production of purified terephthalic acid (PTA), equipment constantly faces severe challenges: high temperature, high pressure, and highly corrosive media such as acetic acid and bromides. Ordinary stainless steel struggles to withstand these harsh environments, while a special material called Hastelloy C-276 becomes the core choice for ensuring the long-term stable operation of the plant.

Hastelloy C-276: What is it?

Hastelloy C-276 is a nickel-based alloy, understood as a high-performance special metal. Its main component is nickel, with the addition of key alloying elements such as molybdenum and chromium. This ingenious combination of elements gives it three core functions:

1. Excellent resistance to general corrosion:
   Effectively resists the direct corrosion of high-temperature concentrated acetic acid, slowing down the wall thinning rate.
2. Excellent resistance to pitting and crevice corrosion:
   Halogen ions, such as bromide, in the medium are the "enemies" of equipment, easily causing localized "perforation" on the metal surface. C-276 effectively resists this localized damage.
3. Strong Resistance to Stress Corrosion Cracking:
   Under the combined action of tensile stress and corrosive media, materials are prone to brittle cracking. C-276 significantly reduces this risk, preventing catastrophic failures.

Simply put, C-276's characteristic is its ability to maintain its integrity and stability even in extremely complex and harsh chemical environments.

Operating Condition Matching: Why PTA Plants Cannot Do Without C-276?

The table below shows the standard proportions of the main chemical components of Hastelloy C-276:

Element	Content (wt%)
Carbon (C)	≤0.010
Chromium (Cr)	14.5 - 16.5
Silicon (Si)	≤0.080
Molybdenum (Mo)	15.0 - 17.0
Cobalt (Co)	≤2.5
Iron (Fe)	4.0 - 7.0
(d)	≤0.040
Tungsten (W)	3.0 - 4.5
Sulfur (S)	≤0.030
Vanadium (V)	≤0.035
Nickel (Ni)	Balance

Understanding the functions of C-276 clearly shows why it is irreplaceable in PTA plants:

01 Coping with PTA Operating Conditions

The core reaction environment of PTA production is high-temperature concentrated acetic acid + bromide. This perfectly matches C-276's expertise in corrosion resistance.

Medium	Solute Concentration (%)	Test Temperature (°C)	Corrosion Rate of Different Alloys (mm/y)
			C-276 Alloy	C-22 Alloy	C-4 Alloy	625 Alloy
Acetic acid	99	Boiling	<0.025	0	0	<0.025
Ferric chloride	10	Boiling	0.05	0.025	3.5	183.1
Formic acid	88	Boiling	0.025	<0.025	0.05	0.225
Hydrochloric acid	1	Boiling	0.325	0.075	0.625	0.025
Hydrochloric acid	1.5	Boiling	0.8	0.35	1.6	8.825
Hydrochloric acid	2	90	0.025	0	0.775	0
Hydrochloric acid	2.5	90	0.3	<0.025	0.85	1.8
Hydrochloric acid + 42 g/L Fe₂(SO₄)₃	1	93	1.025	0.05	--	5.95
Hydrochloric acid + 42 g/L Fe₂(SO₄)₃	5	66	0.125	0.05	0.075	0.05
Hydrochloric acid + 2% HF	5	70	0.65	1.475	0.85	3.075
Hydrofluoric acid	2	70	0.225	0.225	0.425	0.5
Nitric acid	10	Boiling	0.175	<0.025	0.175	0.025
Nitric acid + 1% HCl	5	Boiling	0.2	<0.025	0.275	0.025

02 Ensuring Equipment Integrity

Critical equipment such as reactors, heat exchangers, tower internals, and piping valves in the plant will suffer from pitting or stress corrosion cracking, leading to unplanned shutdowns and huge losses. Using C-276 to manufacture these components eliminates such potential risks directly at the material level, ensuring safe, stable, long-term, full-capacity, and high-quality operation of the plant.

Specific Applications: Key Components in PTA Plants

Due to its superior performance, Hastelloy C-276 is widely used in the core areas of PTA plants with the highest corrosion risk:

1. Oxidation Reactors
   As the "heart" of the entire process, reactors and their internal components (such as agitators and coils) are in direct contact with the most demanding reaction media, making them a typical application area for C-276.
2. Acetic Acid Recovery Systems
   In equipment such as distillation columns, reboilers, and condensers, high-temperature acetic acid vapor is concentrated, exhibiting extremely high corrosiveness. C-276 effectively ensures the long-term operation of this system.
3. High-Temperature Heat Exchangers
   Especially in heat exchangers where process gas and reactants exchange, the tube bundles or plates simultaneously face high temperatures, pressure, and corrosion, making this a key application scenario for C-276.
4. Key Process Piping and Valves
   For pipelines, pumps, and valves transporting reaction products and high-temperature concentrated acetic acid, the use of C-276 can effectively prevent the risk of leakage due to corrosion.

Therefore, the selection of Hastelloy C-276 is an inevitable technical decision based on the specific process conditions of the PTA plant. Through its inherent superior properties, it provides fundamental reliability assurance for the entire production system, making it a truly fundamental material and a key player in modern PTA plants.